fireberd
I've never heard of a CMOS backup battery causing BSOD or system reboots. The only purpose for the battery is to retain the memory (BIOS setup) when the PC is powered off.
Configuration data (ESCD) is also held in CMOS and so is date/time. If there are any processes depending on this it can cause boot errors or BSOD's. I know it's not the first thing that comes to mind but in my case it was the culprit.